Vigils at gravesites, touching, kissing, and making supplications toward them, are the very foundation of shirk

Imam Ibn Taymiyyah [Majmū' Al-Fatāwá, vol. 27, p. 79.]

Imam Ibn Taymiyyah, may Allah have mercy on him, said:

“Keeping vigils at gravesites, touching them [for blessings] kissing them [likewise], making supplications at them [or] toward them, and the like of that are the [very origin and] foundation of shirk¹ and worship of things other than Allāh. It's due to this that the Prophet ﷺ said “Oh Allāh, don't make my grave an object that is worshiped.”²

Majmū' Al-Fatāwá, vol. 27, p. 79.

1. Treating other than Allāh as an equal of Allāh in something that is only for Allāh.

2. Translated by Mikail ibn Mahboob Ariff